DNA methylation promotes Aurora-B-driven phosphorylation of histone H3 in chromosomal subdomains

International audienceConfinement of enzymatic reactions to nuclear and chromosomal subdomains regulates functional organization of the nucleus. Aurora-B kinase regulates cell cycle dependent phosphorylation of chromosomal substrates through sequential localization to a series of sites on chromosomes and the mitotic spindle. In G2 nuclei, Aurora-B recruitment to heterochromatin restricts histone H3S10 phosphorylation to a domain around centromeres (pericentromeres). However, no intrinsic chromosomal determinants have been implicated in Aurora-B recruitment to interphase pericentromeres. Using cyclin B1 as a cell cycle marker, we found that the great majority of nuclei exhibiting H3S10 phosphorylated foci were positive for cyclin B1, thus revealing that H3S10 phosphorylation arises at pericentromeres during late S phase and persists in G2. By immuno-fluorescent in situ hybridization, Aurora-B and H3S10 phosphorylated foci were found more frequently at larger pericentromeres than at smaller ones, revealing a preferential phosphorylation of pericentromeres, exhibiting a high density of methyl cytosines. Disruption of DNA methylation inhibited pericentromeric Aurora-B targeting and H3S10 phosphorylation in G2 nuclei, thus demonstrating the role of DNA methylation in Aurora-B targeting to pericentromeres. These results favour the idea that DNA methylation maintains a local environment essential for regulating the functional properties of sub-chromosomal domains during S-G2 progression

In vivo Study of the Histone Chaperone Activity of Nucleolin by FRAP

Nucleolin is a major nucleolar protein involved in various aspects of ribosome biogenesis such as regulation of polymerase I transcription, pre-RNA maturation, and ribosome assembly. Nucleolin is also present in the nucleoplasm suggesting that its functions are not restricted to nucleoli. Nucleolin possesses, in vitro, chromatin co-remodeler and histone chaperone activities which could explain numerous functions of nucleolin related to the regulation of gene expression. The goal of this report was to investigate the consequences of nucleolin depletion on the dynamics of histones in live cells. Changes in histone dynamics occurring in nucleolin silenced cells were measured by FRAP experiments on eGFP-tagged histones (H2B, H4, and macroH2A). We found that nuclear histone dynamics was impacted in nucleolin silenced cells; in particular we measured higher fluorescence recovery kinetics for macroH2A and H2B but not for H4. Interestingly, we showed that nucleolin depletion also impacted the dissociation constant rate of H2B and H4. Thus, in live cells, nucleolin could play a role in chromatin accessibility by its histone chaperone and co-remodeling activities

The C. elegans HP1 homologue HPL-2 and the LIN-13 zinc finger protein form a complex implicated in vulval development.

International audienceHP1 proteins are essential components of heterochromatin and contribute to the transcriptional repression of euchromatic genes via the recruitment to specific promoters by corepressor proteins including TIF1 and Rb. The Caenorhabditis elegans HP1 homologue HPL-2 acts in the "synMuv" (synthetic multivulval) pathway, which defines redundant negative regulators of a Ras signaling cascade required for vulval induction. Several synMuv genes encode for chromatin-associated proteins involved in transcriptional regulation, including Rb and components of the Mi-2/NuRD and TIP60/NuA4 chromatin remodeling complexes. Here, we show that HPL-2 physically interacts in vitro and in vivo with the multiple zinc finger protein LIN-13, another member of the synMuv pathway. A variant of the conserved PXVXL motif found in many HP1-interacting proteins mediates LIN-13 binding to the CSD of HPL-2. We further show by in vivo localization studies that LIN-13 is required for HPL-2 recruitment in nuclear foci. Our data suggest that the LIN-13/HPL-2 complex may physically link a subset of the Rb related synMuv proteins to chromatin

Nucleolin Interacts and Co-Localizes with Components of Pre-Catalytic Spliceosome Complexes

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Un nouveau cadre conceptuel pour l’infirmité motrice cérébrale

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Reduction of an electronic card thermal problem by the modal sub structuring method

International audienceThe computation time needed to compute modes remains the main drawback of modal methods. This computation time can be reduced by using the sub structuring modal method. First of all, the model is divided into elementary entities, and modes of each entity are independently computed. In order to solve the original problem, only specific modes are chosen to couple sub-structures together: the Steklov modes. This method is applied to an electronic card witch supports eighteen components. The Printed Circuit Board is accurately modeled considering local thermal properties (like local copper tracks). The reduced model recovers the maximum temperature of critical component for a dynamic scenario and various boundary conditions reducing the solver time by 500

Un nouveau cadre conceptuel pour l'infirmité motrice cérébrale.

Cerebral palsy was recently redefined as a group of disorders of the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication or behaviour, by epilepsy or by secondary musculoskeletal problems (Bax et al. 2005). It has an estimated incidence of 0.2 %, i.e. 200 new cases per year in Belgium and a total of about 18,000 patients (in a population of 10 millions). Over the last few years, interest has risen in issues pertaining to learning, social participation, services, some assessment modalities (including gait analysis), some therapeutic modalities (including orthotics and antispastic treatment). The Department of Neurology of the H6pital Universitaire des Enfants Reine Fabiola has taken an active part in several aspects of these developments, including research on pathophysiology, neurophysiology, motor control and management (including intrathecal baclofen) as well as setting up the Interuniversity Reference Centre for Cerebral Palsy ULB-VUB-ULg. The 20th anniversary of the hospital offers an opportunity to review this important topic.SCOPUS: ar.jinfo:eu-repo/semantics/publishe